I assume this is 9 mm Luger. If it is one of the other 9 mm rounds, you need to say so.

What is the length of that bullet? You want to match the seating depth for a similar bullet that has load data available. To do that you will also need the length of that known load data bullet. There is a partial list, here. For the load data cartridge, find the seating depth as follows:

Seating Depth = Standard Case Length + Bullet Length - COL

Once you have that seating depth for the known data load, you can match it with your bullet by rearranging the above and putting in your Winchester bullet length:

COL = Standard Case Length + Bullet Length - Desired Seating Depth

Load a dummy (bullet in sized case; no powder or primer) and check that it drops into the chamber without interference of the bullet in the lands (plunk test), then reassemble the gun and put it in the magazine and rack the slide to be sure it feeds OK. If you find it passes both those tests, then begin with the other bullet's starting load.

If it doesn't pass one of the above tests, you'll probably have to seat the bullet deeper. That will mean reducing the powder charges further. At that point I would look for a bullet that is the same length and that has load data that shows the same COL you calculated and use it's load data. The Lyman manual also has somewhat more generic load data that tends to allow for this. Whatever you end up with, just don't skip using the lowest load first. Work up while watching for pressure signs.